The molecular cloning in a plasmid of E. coli of genes of E. coli, and of micronuclear genes and rRNA genes of the protozoon Tetrahymena are being carried out. The cloned Tetrahymena genes will be used to study the formation of the macronucleus and of amplified rDNA. Attempts will be made to clone specific vertebrate genes, including genes coding for immunoglobulins. BIBLIOGRAPHIC REFERENCES: Helling, Robert B., 1975. Eukaryotic Genes in Prokaryotic Cells. Stadler Genetics Symp. 7: 15-36. Lakshmi, T.M., and Robert B. Helling, 1976. Selection for citrate synthase-deficiency in icd mutants of Escherichia ccli, J. Bacteriol., submitted for publication.